Ion-implanted magnetic bubble memories are disclosed in U.S. Pat. No. 3,792,452 of M. Dixon et al., issued Feb. 12, 1974 and U.S. Pat. No. 3,828,329 of R. F. Fischer et al., issued Aug. 6, 1974. In such memories, propagation paths for bubbles are defined by unimplanted regions in the otherwise implanted host layer. Bubbles reside in the implanted region and propagate along the boundary between implanted and unimplanted regions in response to the rotation of an in-plane magnetic drive field. Typically, the unimplanted regions have a contiguous disc geometry, forming a propagation path of interlaced bulges and cusps.
The first of the above-mentioned patents shows the familiar major-minor bubble memory organization. This organization is characterized by a plurality of closed loop propagation paths termed "minor loops" and at least one "major" path. A bubble generator and detector are associated with the major path and data (magnetic bubbles) move between the ends of the minor loops and the major path typically at transfer gates.
Transfer gates generally are defined by an electrical conductor which, when pulsed, causes bubbles to move to one end of the minor loops from associated positions on the major path. There are disadvantages associated with the conventional conductor controlled transfer gates. Long conductor lines, necessary in large chips, are not desirable because of yield loss due to conductor defects, and the need for high voltage pulse generators. Also, there may be stress related conductor crossing problems and the conductor must be precisely aligned with specific portions of the implant pattern to achieve transfer.